Some Facts
As an ASO she will be non commissioned and part of TG12. If she wishes to transfer to ATC that is TG9 and that kind so transfer is very uncommon. There is work ongoing to merge the two but I don't think it is imminent. If she wants to go ATC in the future then she should apply now and look at either going for a Commission or looking at direct entrant SNCO Controller (An ATC Officer can give more info on that).
The ABM Branch does offer fast track to SNCO Controller after several years service. You do the full course in present rank (SAC or NCO) and get promoted to SGT on successful completion.
Main first tour jobs for ASO are at Boulmer and Scampton. She will go to the Falklands at least once in each rank. Thereafter there are numerous jobs for ASOs in various units and out of Branch posts.
Risk? Yes, it is the military. Will she be sent to different places? Yes, it is the military. Will she have a say? Yes but at the end of the day you go where you are sent. If she has even the slightest problem with any of that then I really do not think the RAF is for her. We have absolutely no shortage of very keen applicants. Sorry, but those are the facts. I wish her the very best in making the right choice.